The present invention relates to a digital broadcast receiver for receiving a digital broadcasting program via a broadcasting satellite (BS) and, more specifically, to the receiver provided with a control system capable of adaptively controlling the broadcast reception when a short break of a RF-signal occurs due to changing a transmitting station to another at the receiver or due to discontinuity of signal by changing a transmitting system at the transmission station.
A short break of a RF-signal can be noticed in advance by using a transmission control signal multiplexed with a digital broadcasting signal via a BS. However, there has been no idea of adaptive control of the receiver to smoothly restoring the broadcast reception against a immediately ceasing short break (wave discontinuity) of a broadcasting signal, which may occur without the notice when a transmission system is changed to another at a broadcast transmitting station. A receiver provided with means for realizing the above-mentioned idea has not yet proposed.
In other words, no proposal has been made in regard to a receiver controlling method that, when a broadcast signal is instantaneously broken (with discontinuity) and immediately restores itself to normal state, can adaptively control the reception of the broadcast by re-synchronizing and presenting video-and-audio signals. A broadcasting wave may suffer attenuation by the effect of some local surrounding conditions such as a heavy rainfall, resulting in decreasing the signal-to-noise ratio of the signal. The short break of a broadcasting signal may take place when, to improve the C/N ratio in such a situation, a viewer at a receiver changes a current received transmitting station to another or an operator at a transmitting station changes a current transmitter to another.
There has not yet been proposed a receiver that has means for discriminating whether a signal is instantaneously broken (it may be restored to normal state after a very short period) or broken (no signal is transmitted for a long time for some reason) and control means adapted to realizing prompt pull-in for re-synchronization and smooth returning presentation of normal video-audio signals after ceasing of the short break.
Once a signal was broken, a conventional receiver, taking no consideration of whether signal can be restored with a short break, detects the out-of-synchronization, stops presentation of an image, mutes the sound output, searches a tunable frequency, retunes and restarts reception of data (e.g., service information in the MPEG2 and the so on). In other words, the receiver performs substantially the same process as it must perform after turning on its power supply.
If it is previously known that the signal will be instantaneously broken and immediately restored to the normal state, the receiver desirably maintains acquired data and state until the broken signal is restored to its normal state. This enables the receiver to promptly restart normal video/audio presentation, i.e., to return to the normal operation.
Accordingly, a receiver that can detect an instantaneously restorable short-break or discontinuity of a broadcasting signal and perform a specially designated process enabling a viewer to look and listen the video-audio presentation without sensing the actual short-break (discontinuity) of a signal.
In practice with a short-break of a signal, the receiver detects it, keeps in its memory acquired data and receiving conditions until a continuous signal is restored and, then, optimally controls the returning process to promptly restart the normal audio-video presentation. Namely, the present invention has as its primary object the provision of a receiver that can promptly restore the presentation of normally restored signal with a possibly shortest break (discontinuity) that cannot be sensed by the viewer. This receiver can thus solve the problem of the prior art receiver that has to perform a prolonged restart process substantially corresponding to its start process beginning at turning on its power supply.
The receiver detects a break or discontinuity of a received signal and discriminates whether it prolongs or whether it is a short break by a transmission control signal multiplexed with a digital broadcasting wave. According to the discrimination result, the receiver holds tuning data such as a center frequency of a tuner and a frequency offset and controls closed-loop transmission functions of carrier and clock (clock signal) of a phase shift keying (PSK) demodulating portion to obtain a wider pull-in range and a shorter lock-up time. It holds information on an error of phase shift between an internal counter and a program clock reference (PCR) of a digital phase locked loop (PLL), stops updating of information by decoding a video image and presents an immediately preceding image signal. Furthermore, the receiver stops detecting and updating of a presentation time stamp (PTS) and the PCR, changes a jitter range for PCR according to received C/N and controls itself so as to promptly transit to normal operation after a short-break.
The receiver can thus operate to minimize the disordered audio-visual presentation to the viewer due to the discontinuity of the signal during the returning process.
The present invention is provided with the following technical means:
(1) Accordingly, an object of the present invention is to provide a digital broadcast receiving system for receiving a transport stream transmitted according to the MPEG standard and presenting decoded broadcast information comprising: a synchronization detecting means for detecting a synchronizing code in the transport stream; a short-break discriminating means for discriminating whether a transport stream suffers a short-break or not according to synchronizing-code lacking duration determined from the synchronizing-code detection made by the synchronization detecting means; and a returning process control means for performing a process of returning to normal operation after ceasing a short-break of the broadcasting wave by controlling at least one of: means for holding tuning information of a tuner; means for controlling closed-loop transmission functions of carrier and clock of demodulating portion; means for holding phase error information of a digital phase-locked loop (PLL) according to a program clock reference (PCR); means for stopping updating the decoded image presentation and presenting an immediately preceding image signal; means for stopping detecting/updating a presentation time stamp (PTS); and means for stopping detecting/updating the PCR and changing a jitter range for the PCR, wherein the normal operation of the receiving system after ceasing a short-break of the transport stream is restored by driving the returning process control means according to a result of discrimination made by the short-break discriminating means.
(2) Another object of the present invention is to provide a digital broadcast receiving system for receiving a digital broadcasting wave and presenting demodulated broadcasting information comprising: a transmission control signal detecting means for detecting a transmission control code multiplexed with the digital broadcasting wave; a frame synchronization detecting means for detecting a frame synchronizing signal in the digital broadcasting wave; a short-break discriminating means for determining whether the broadcasting wave suffers a short-break or not according to synchronization lacking duration determined from a result of detection made by the short-break discriminating means; a short-break pre-announcing means for giving notice of a short-break of a digital broadcasting wave by a content of the transmission control signal detected by the transmission control signal detecting means; and a returning process control means for performing a process for returning to normal operation after ceasing a short-break of the digital broadcasting wave by controlling at least one of: means for holding tuning information of a tuner; means for controlling closed-loop transmission functions of carrier and clock of a phase-shift keying (PSK) demodulator; means for holding a phase error information of a digital phase-locked loop (PLL) according to a program clock reference (PCR); means for stopping updating the decoded image presentation and presenting an immediately preceding image signal; means for stopping detecting/updating a presentation time stamp (PTS); and means for stopping detecting/updating the PCR and changing a jitter range for the PCR, wherein the normal operation of the receiving system after ceasing a short-break of the broadcasting wave is restored by driving the returning process control means according to a result of discrimination made by the short-break discriminating means or a result of the notice made by the short-break pre-announcing means.
(3) A further object of the present invention is to provide a digital broadcast receiving system for receiving a digital broadcasting wave and presenting demodulated broadcasting information comprising: a transmission control signal detecting means for detecting a transmission control signal multiplexed with the digital broadcasting wave; a closed loop detecting means for detecting a pull-in state of closed loop of a clock or a carrier of a phase-shift keying demodulator; a short-break discriminating means for discriminating whether the broadcasting wave suffers a short-break or not according to a closed-loop""s pull-in state and duration detected by the closed loop detecting means; a short-break pre-announcing means for giving notice of a short-break of a digital broadcasting wave by a content of the transmission control signal detected by the transmission control signal detecting means; and a returning process control means for performing a process of returning to normal operation after ceasing a short-break of the digital broadcasting wave by controlling at least one of: means for holding tuning information of a tuner; means for controlling closed-loop transmission functions of carrier and clock of a phase-shift keying (PSK) demodulator; means for holding phase error information of a digital phase-locked loop (PLL) according to a program clock reference (PCR); means for stopping updating the decoded image presentation and presenting an immediately preceding image signal; means for stopping detecting/updating a presentation time stamp (PTS); and means for stopping detecting/updating the PCR and changing a jitter range for the PCR, wherein the normal operation of the receiving system after ceasing a short-break of the broadcasting wave is restored by driving the returning process control means according to a result of discrimination made by the short-break discriminating means or a result of the notice made by the short-break pre-announcing means.
(4) A still further object of the present invention is to provide a digital broadcast receiving system for receiving a digital broadcasting wave and presenting demodulated broadcasting information comprising: a transmission control signal detecting means for detecting a transmission control signal multiplexed with the digital broadcasting wave; a short-break discriminating means for determining whether the broadcasting wave suffers a short-break or not according to logic of the transmission control signal detected by the transmission control signal detecting means; and a returning process control means for performing a process of returning to normal operation after ceasing a short-break of the broadcasting wave by controlling at least one of: means for holding tuning information of a tuner in specified time after the short-break; means for controlling closed-loop transmission functions of carrier and clock of a phase-shift keying (PSK) demodulator; means for holding phase error information of a digital phase-locked loop (PLL) according to a program clock reference (PCR); means for stopping updating the decoded image presentation and presenting an immediately preceding image signal; means for stopping detecting/updating a presentation time stamp (PTS); and means for stopping detecting/updating the PCR and changing a jitter range for the PCR, wherein the normal operation of the receiving system after ceasing a short-break of the broadcasting wave is restored by driving the returning process control means according to a result of discrimination made by the short-break discriminating means.